cmd/coordinator: a few fixes
cmd/coordinator: a few fixes

- record 'go list' failures in sub-repos as test failures.
- don't try to run sharded tests on old go 1.4 trees.
- improved logging.

Change-Id: Ia0ca72caf5fc02cddfefdd1c87d68108901a16be
Reviewed-on: https://go-review.googlesource.com/14284
Reviewed-by: Andrew Gerrand <395a7d33bec8475c9b83b7d440f141bcbd994aa5@golang.org>

golang/build,golang/build,proppy/build,proppy/build,proppy/build,proppy/build,golang/build,golang/build